In an ideal differential amplifier system, two input signals are in inverted phases, meaning that two differential power transistors are not simultaneously turned on. However, due to the process, voltage and temperature (PVT) variation effects, phases of the two input signals may not be precisely controlled so that the two differential power transistors are simultaneously turned on, thereby a cross-over current (i.e. overlapped current) is generated. The cross-over current can be regarded as a dissipated current, and only contributes power loss. In addition, when a feedback loop is applied to control a gain of the amplifier, the cross-over current may affect an accuracy of the gain control.